Při přemokření začne pokojová rostlina vadnout.

Here při means something like in the case of, under conditions of, or when there is.

So při přemokření is roughly:

• when overwatered
• in case of overwatering
• under waterlogged conditions

It does not literally mean a person is actively watering the plant at that moment. It describes the condition of too much water.

Czech often uses a noun phrase where English might prefer a whole clause.

• při přemokření = in case of overwatering / when overwatered
• když se přemokří = when it gets overwatered

The version with při + noun sounds compact and a bit more neutral or informational, which is common in instructions, care guides, and technical descriptions.

After při, Czech normally uses the locative case.

So přemokření is in the locative here.

A useful thing to know: many neuter nouns ending in -í have the same form in several singular cases, so the locative may look identical to the dictionary form. That is why you do not see an obvious ending change here.

Přemokření is a verbal noun built from a verb meaning to overwater / to soak too much / to make too wet.

So instead of saying the plant is overwatered with a verb, Czech uses the noun overwatering / excessive wetness / waterlogging.

This kind of noun is very common in Czech, especially in formal or descriptive language.

Začne is the 3rd person singular form of začít, meaning to begin / to start.

It agrees with the subject pokojová rostlina because that subject is:

• singular
• feminine

In English we say the houseplant starts to wilt. Czech expresses that with začne vadnout.

This is mostly about aspect.

• začít is perfective
• začínat is imperfective

In this sentence, Czech is talking about the moment the process begins, so začne is very natural.

Even though začne is formally a present-tense form, perfective present forms often have a future-like meaning. In a general statement like this, English still often translates it with a present:

• Při přemokření začne pokojová rostlina vadnout.
• When overwatered, a houseplant starts to wilt.

If you used začíná, it would feel more like describing an ongoing situation or repeated observation from the inside of the process.

After začne, Czech normally uses an infinitive describing the process that begins.

• vadnout = to wilt as a process
• uvadnout = to wilt completely / to become wilted

Here the meaning is it begins to wilt, so the imperfective vadnout is the best choice.

So:

• začne vadnout = will start wilting
• uvadne would mean more like it will wilt fully

Pokojová rostlina is the normal Czech term for a houseplant or indoor plant.

Literally:

• pokojová = room-related / for a room
• rostlina = plant

So it does not just mean any plant that happens to be in a room once. It is the standard category name for a plant kept indoors.

Because it is an adjective agreeing with rostlina.

Rostlina is:

• feminine
• singular
• nominative

So the adjective must match it:

• pokojová rostlina

This is standard Czech adjective-noun agreement.

Czech has no articles.

So pokojová rostlina can mean:

• a houseplant
• the houseplant
• sometimes just houseplants in a general sense, depending on context

You understand which one is meant from the situation, not from an article like in English.

No, Czech word order is fairly flexible.

This sentence starts with Při přemokření to highlight the condition first:

• Při přemokření začne pokojová rostlina vadnout.

You could also say:

• Pokojová rostlina začne při přemokření vadnout.

That is also grammatical, but it sounds a little less natural if the main point is the condition. The original order is good for explanatory or instructional style.

Yes, slightly.

The phrase při přemokření sounds a bit more like:

• a care guide
• an explanation in a book
• an informational statement

In everyday speech, many people might say something more direct, for example:

• Když ji přelijete, začne vadnout.
• Když je moc mokrá, začne vadnout.

So the original sentence is natural, but it has a somewhat neat, informative style.

The difficult part is ř, which is a special Czech sound.

A practical learner-friendly approximation:

• při sounds a bit like przhi said very quickly

More exactly:

• p as in English spin
• ř is a Czech sound somewhere between r and zh
• i like ee in see

You do not need a perfect ř immediately. If you say something close to przhi, Czech speakers will usually understand you.